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Two-Field Quintom Models in the w ? w Plane

Zong-Kuan Guo; Yun-Song Piao; Xinmin Zhang; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The w?w′ plane, defined by the equation of state parameter for the dark energy and its derivative with respect to the logarithm of the scale factor, is useful to the study of classifying the dynamical dark energy models. In this note, we examine the evolving behavior of the two-field quintom models with w crossing the w = ?1 barrier in the w ? w′ plane. We find that these models can be divided into two categories, type A quintom in which w changes from > ?1 to < ?1 and type B quintom in which w changes from < ?1 to > ?1 as the universe expands. |

submitted time
2017-09-27
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Cosmological Evolution of a Quintom Model of Dark Energy

Zong-Kuan Guo; Yun-Song Piao; Xinmin Zhang; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We investigate in this paper the cosmological evolution of a dark energy model with two scalar fields where one of the scalar has canonical kinetic energy and another scalar has negative kinetic energy term. For such a system with exponential potentials we find that during the evolution of the universe the equation of state w changes from w > ?1 to w < ?1, which is consistent with the recent observations. A phase-plane analysis shows that the “phantom”-dominated scaling solution is the stable late-time attractor of this type of models. |

submitted time
2017-09-27
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Attractor Behavior of Phantom Cosmology

Zong-Kuan Guo; Yun-Song Piao; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We investigate the cosmological attractor of the minimally coupled, self-interacting phantom field with a positive energy density but negative pressure. It is proved that the phantom cosmology is rigid in the sense that there exists a unique attractor solution. We plot the trajectories in the phase space numerically for the phantom field with three typical potentials. Phase portraits indicate that an initial kinetic term decays rapidly and the trajectories reach the unique attractor curve. We find that the curve corresponds to the slow-climb solution. |

Cosm ologicalScaling Solutions and C ross-couplingExponentialPotential

Zong-Kuan Guo; Yun-Song Piao; Rong-Gen Cai; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We present a phase-space analysis of cosmology containing multiple scalar elds with a positive or negative cross-coupling exponential potential. We show that there exist power law kinetic-potential-scaling solutions for a sciently at positive potential or for a steep negative potential.The former is the unique late-ti e attractor, but it is difficult to yield assisted ination.Thelaterisneverstablein an expanding universe.M oreover,fora steep negative potentialthere existsa kinetic-dom inated regim e in which each solution isa latetime attractor. In the presence ofordinary m atterthese scaling solutionswith a negative cross-coupling potentialare found unstable. W e briey discuss the physicalconsequences of these results. |

Inflationary Attractor from Tachyonic Matter

Zong-Kuan Guo; Yun-Song Piao; Rong-Gen Cai; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We study the complete evolution of a flat and homogeneous universe dominated by tachyonic matter. We demonstrate the attractor behaviour of the tachyonic inflation using the Hamilton-Jacobi formalism. We else obtain analytical approximations to the trajectories of the tachyon field in different regions. The numerical calculation shows that an initial non-vanishing momentum does not prevent the onset of inflation. The slow-rolling solution is an attractor. |

Cosmological Scaling Solutions and Multiple Exponential Potentials

Zong-Kuan Guo; Yun-Song Piao; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We present a phase-space analysis of cosmology containing multiple scalar fields with positive and negative exponential potentials. We show that there exist power-law multi-kinetic potential scaling solutions for sufficiently flat positive potentials or steep negative potentials.The former is the unique late-time attractor and the well-known assisted inflationary solution, but the later is never unstable in an expanding universe. Moreover, for steep negative potentials there exist a kinetic-dominated regime in which each solution is a late-time attractor. We briefly discuss the physical consequences of these results. |

CMB anomalies from an inflationary model in string theory

Zhi-Guo Liu; Zong-Kuan Guo; Yun-Song PiaoSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Recent Planck measurements show some CMB anomalies on large angular scales, which confirms the early observations by WMAP. We show that an inflationary model, in which before the slow-roll inflation the Universe is in a superinflationary phase, can generate a large-scale cuto? in the primordial power spectrum, which may account for not only the power suppression on large angular scales, but also a large dipole power asymmetry in the CMB. We discuss an implementation of our model in string theory. |

Obtaining the CMB anomalies with a bounce from the contracting phase to inflation

Zhi-Guo Liu; Zong-Kuan Guo; Yun-Song PiaoSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Recent Planck data show the anomalies of CMB fluctuations on large angular scales, which confirms the early observations by WMAP. We continue studying an inflationary model, in which before the slow roll inflation the universe is in a contracting phase, and fit the model with the Planck data. It is showed that this model may generate not only the power deficit at low-l, but also a large hemispherical power asymmetry in CMB. We also discuss the implication of the result to the eternal inflation scenario. |

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